Test flannel for shrinkage. Cut a 2 or 3 inch square and wash as you intend to do for the finished quilt. When dry, measure the squares to see if they are the smaller. If they are, prewash the fabric before sewing.

I made this blanket for my niece using a paper piece pattern I drew . The center of the square is the left over flannel I used for her burp cloths.
https://amye116sewingprojects.shutterfly.com/pictures/34#35
A closer look https://amye116sewingprojects.shutterfly.com/pictures/34#34
The flannel was easy to work with. I love the way it turned out.
Good luck with your project

Thank you :). Yes I did prewash and gave it a quick press before I started.... since I was paper piecing I knew I would be pressing every seam as I went so I didn't spend a bunch of time pressing before hand.

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